Which of the following is a characteristic of x-rays?

X-rays are a form of electromagnetic radiation, which allows them to travel in straight lines. This characteristic is significant because it affects how X-rays interact with matter, including how they pass through various substances in diagnostic imaging. The straight-line travel of X-rays is essential for creating clear images; it ensures that the beam can be directed precisely toward the area of interest, producing accurate and interpretable results.

The other characteristics do not accurately describe X-rays. For instance, X-rays do not have mass since they are photons, which are massless particles. Additionally, X-rays are not electrically charged; they are neutral radiation. Finally, X-rays can penetrate matter rather than being unable to do so; their penetrating power is what allows them to pass through soft tissues while being absorbed by denser materials like bone, enabling the formation of diagnostic images.